The present invention is directed to a closed ring-shaped reinforcing member for use in concrete where the member is stressed by annular tensile forces.
In a bundled prestressing member for prestressed concrete, the individual parts of the member, such as steel wires or strands, in the region between their anchorages are positioned as closely together as possible with only a minimum distance between them. The individual parts are spread out in a fan-shaped manner as they approach the anchorage since in the anchorage a larger space between the parts is required. At the location where the individual parts commence to be spread apart, deflecting forces directed radially outwardly are developed and such forces produce transverse tensile stresses in the concrete structure and such stresses can result in cracks. To absorb these deflecting forces it is known to arrange an additional reinforcement, such as a spiral shaped member, in the region where the deflection of the parts takes place. The installation of such a spiral shaped member involves additional effort, particularly because the spiral shaped member must be maintained at a certain distance from the prestressing member.
Further, it is known to provide a steel deflection ring in place of a spiral shaped member as the reinforcing member so that it absorbs the deflection forces as annular tensile forces. Under the action of the annular tensile forces, the deflection ring stretches, particularly in slender structural members, so that there exists the danger of cracks developing which require additional reinforcement.
Similar problems exist in prestressed member anchorages. In such anchorages it is known to use a bell-shaped anchoring body for individual as well as bundled prestressed members. The anchoring body includes an inclined recess face for an anchoring nut or an anchoring plate and includes an annular or tubular body with a cylindrical cross-section for absorbing transverse tensile stresses, note Austrian Patent No. 217 194.
In bell-shaped anchorages, the stretching of the annular body, because of the high forces acting in the concrete enclosed within it, can become so great that cracks develop in the region of the concrete structure around the anchorage. In particular in slender structures, such as slender girders, the development of cracks may endanger the important anchorage due to corrosion by the passage of harmful air and moisture through the cracks.